The apparatus in this invention is characterized by gas entries located in the bottom; usually in the related art, the gas entrance is at the top and the outlet is at the bottom; The disadvantage of having descendant flow is that at the bottom the reactor usually has a very bad gas flow, which requires in this zone an inert material, reducing the operation space in the reactor which causes problems with subsequent separations of this inert material from sponge iron.
Another disadvantage of the known art is that the gas recollection is achieved by a plenum in frustum-conic form which is usually metallic and must be cooled with water by a coil. In the fixed bed reactors with descendant flow, there are in the plenum exit particle entrainment due to the high velocity of the gas reached at this points.